In general, this invention relates to improved electrical leads. More particularly it relates to improved leads for implantable pulse generators (IPG's) such as heart pacemakers. Heart pacemakers may have one or more leads incorporating this invention. Such implantable medical devices require elongate electrical leads which attach to sites in the body for electrical contact therewith. The surfaces of the leads often contact each other and rub against each other. In the case of transvenous heart pacemakers which are implanted in the chest, a pair of leads may extend through a blood vessel into the heart for interior attachment thereto. The two leads extend through a common vessel for some portion of their entry path and rub against each other in various surface areas.
It has become common practice to include silicone rubber as a surface covering for such leads because it is biocompatible and biostable. It is particularly common to utilize silicone rubber tubing for this purpose. A continuing problem with the use of silicone rubber has been the binding which occurs when these outer coverings rub against each other. Such binding is often referred to as "surface blocking" or simply "blocking" Implantation side-by-side thus has been found to give rise to sticking and even dislodgment of the leads.
Various surface coatings have been tried in an effort to reduce "blocking" and improve the "slip" of silicone rubber. However, such coatings have been found to have too short a lifetime or to lack biocompatibility and/or biostability.
It is a specific object of this invention to provide silicone rubber with improved surface properties in this regard and particularly to provide silicone rubber tubing and coverings for leads and in combination with leads which exhibit permanent and improved "blocking" and "slip."